Processes for incorporating ground tire rubber into bituminous material to make asphalt cement systems suitable for paving, roofing and other uses have hitherto been unduly complex and thus costly in use. Known processes use additional constituents of the composition and additional process steps in an attempt to provide a homogenous system. Such attempts have not been successful.
Applicant's prior patent applications have been directed to air blown compositions of ground tire rubber and distillation tower bottoms. In these processes, some of the aromatic oils are lost due to dehydrogenation resulting in an oxidized product which, while fully integrated, is more suitable for applications requiring roofing grade material than for applications requiring paving grade asphaltic material.
Duong et al., U.S. Pat. No. 5,270,361, is directed to a process for making an asphalt composition which includes synthetic or natural rubber which may be in particles of up to one-half inch in thickness. Elemental selenium or an organo-selenium compound is added into the mixture to act as a substitute for the sulfur which is removed during the vulcanization process. The selenium or organo-selenium compound acts as a cross-linking agent. The composition is treated with pressurized air in a dehydrogenation reaction. In the dehydrogenation vessel, the dispersing device includes a pair of discs turning at 3600 rpm which promotes homogenization and acceleration of the dehydrogenation reaction. Elemental selenium or an organo-selenium compound is added into the homogenized composition and mixed in a static mixer. The asphalt composition is then recovered and stored in a container at about 150.degree. to 175.degree. C.
Wilkes, U.S. Pat. No. 4,609,696, describes a rubberized asphalt composition which is made by combining asphalt with a hydrocarbon oil to provide a homogenized asphalt-oil mixture or solution, combining the mixture with particulate rubber to provide a homogenous gel and emulsifying the gel by passing the asphalt-rubber-oil gel, with water, through a colloid mill.
Oliver, U.S. Pat. No. 4,430,464, describes a pavement binder composition in which rubber particles are digested in a bituminous material.
Pagen et al., U.S. Pat. No. 4,588,634 describes a roofing material using bitumen and ground tire rubber together with mineral stabilizer and an elastomeric polymer composition.
Rouse, U.S. Pat. No. 5,334,641, describes a rubber modified asphalt for use as a paving compound which is formed by reacting ground rubber, of 50 mesh or finer, with paving grade asphalt and mixing the combination at 300.degree.-400.degree. F. The mixture reacts fully within 25 minutes or less to form a freely pouring mixture and can be held at normal asphalt working temperatures for at least 96 hours without degradation.
Davis, U.S. Pat. No. 4,485,201, describes a method of modifying asphalt with a mixture of ground rubber and synthetic rubber. The compositions include oils and antioxidants in addition to asphalt and rubber. The processing takes place below 375.degree. F.
McDonald, U.S. Pat. No. 4,085,078, describes a paving material formed by heating a mixture of paving grade asphalt and a non-oil resistant rubber to a temperature of about 360.degree. F. to 500.degree. F. The asphalt rubber mixture is diluted with a diluent prior to reaction to form a gelled reaction product. McDonald, U.S. Pat. No. 4,069,182, also describes a hot gelled composition which can be applied to cracked or distressed pavements to repair such pavements. McDonald, U.S. Pat. No. 3,891,585, describes a similar hot gelled composition for repairing pavements.
Winters et al., U.S. Pat. No. 3,919,148, describes an elastomeric paving material prepared from asphalt, rubber and an asphalt solvent to form a hot, thick, viscous, gelled composition.
None of these prior art disclosures describe a process for incorporating whole tire rubber into an asphalt medium, without oxidation or air blowing, as described below.